Romain Barres, a genetic scientist from the University of Coppenhagen, and his colleagues conducted this study with 13 "lean" men with a median body mass index (BMI) of 23, and 10 "obese" men with a median BMI of 32. To further explain BMI, a man who is 180 cm and 75 kg has a BMI of 23 and a man of the same height who has a BMI of 32 weighs 104 kg. The scientists then obeserved different epigenetic markers of the patients sperm. What they found were that the gene methylation patterns of the sperm differed between the two groups of men. Gene methylation is a determining factor in whether or not a gene is turned on. About 9000 genes were found to be methylated depending on the group, lean or obese, the patient was in. Most of those genes were related to brain development, appetite control, and metabolism.
To further explain whether weight loss will or will not affect a persons epigenetic markers they ran an experiment with six men who are about to undergo gastric bypass surgery. Prior to surgery the scientists collected sperm samples and then another sample a week later. Their results show that epigenetic changes can happen very quickly because of the differences in methylation in 1509 genes. A year later when their weight reached a stable level another sample was collected and they found 3910 gene changes.